Many states have their own regulations governing illegal immigrants. And five states have introduced bills similar to Arizona's SB 1070, which is the target of a federal lawsuit.

Washington state Rep. Sharon Tomiko Santos said that although immigration falls under the federal government's jurisdiction, states are responsible for illegal immigrants living within their borders. States have to pay the bulk of the cost for education, healthcare and incarceration of illegal immigrants, and they must help newcomers integrate.

Santos said the conflicting laws from state to state can create confusion. For example, a company may have offices in two states — in one that requires employment verification and in one that doesn't. "It is exactly those kinds of issues that need to be worked out at the federal level so that there is no question across the 50 states as to what the rules are," she said.

Santos said states generally agree that the enforcement of civil immigration policy is a federal responsibility. "It is not a responsibility that states necessarily want," she said.

But Federation for American Immigration Reform President Dan Stein said immigration policy is inevitably a partnership between states and the federal government. The states are "the keys to the kingdom" — where immigrants get identification documents, services and jobs, he said.

"If you try only to control immigration at the border … it's an exercise in futility," he said. "National immigration policy can only be carried out with the participation of the states."